The present invention relates to an electric power converter circuit including an AC to DC converter circuit for improving the input power factor and for suppressing higher harmonics, and a DC to AC converter circuit for performing DC to AC conversion.
FIG. 6 is a block circuit diagram of a conventional electric power converter circuit including a power factor improving circuit as described in Japanese Patent Publication No. 2005-110434 and a DC to AC converter circuit. FIG. 7 is a wave chart describing the operations of the conventional electric power converter circuit.
In FIG. 6, an AC power supply 1, coils 2, 3, capacitors 4, 5, a transformer 6, switching devices 11 through 15, and diodes 21 through 27 are shown. In detail, the power factor improving circuit (an AC to DC converter circuit) is formed of a rectifying circuit, including diodes 21 through 24, and switching device 15. A DC to DC converter circuit (a DC to AC converter circuit+an AC to DC converter circuit) is formed of a converter circuit having a full-bridge structure and a rectifying and smoothing circuit including diodes 26, 27 and capacitor 5.
As switching device 15 in the power factor improving circuit turns ON while the voltage of the AC power supply 1 is positive, a current flows from AC power supply 1 to AC power supply 1 via diode 21, coil 2, switching device 15, and diode 24, increasing the current i2 of coil 2. As switching device 15 turns OFF while the voltage of AC power supply 1 is positive, a current flows from coil 2 to coil 2 via diode 25, capacitor 4, diode 24, AC power supply 1 and diode 21, decreasing the current i2 of coil 2. When the voltage of AC power supply 1 is negative, diodes 23 and 22 are electrically conductive in substitution for diodes 21 and 24, resulting in the similar operations as described above. Due to the above described operations of the power factor improving circuit, it is possible to control the current i2 and the input current by changing the gate signal vG15 for switching device 15 as described in FIG. 7. Therefore, it is possible not only to improve the input power factor and reduce the input current higher harmonics but also to obtain a DC voltage (the voltage of capacitor 4) from an AC input voltage.
In the DC to DC converter circuit described above, the voltage generated across capacitor 4 is applied to transformer 6 via switching devices 11 and 14, when switching devices 11 and 14 are ON, and rectified on the secondary side of transformer 6. Thus, a DC voltage (the voltage of capacitor 5), insulated from AC power supply 1, is obtained. In the same manner, as switching devices 13 and 12 turn ON, a negative voltage is applied to transformer 6 and an energy is fed to the secondary side thereof. When a high-frequency AC voltage is applied to a transformer, the method as described above, which converts a DC to an AC and further coverts the AC to a DC, is employed very often for reducing the transformer size.
It is necessary for the electric power converter circuit, as described in FIG. 6, to employ many constituent parts, causing problems for reducing the size, weight and manufacturing costs of the electric power converter circuit.
In view of the foregoing, it is an object of the invention to provide an electric power converter circuit that facilitates reducing the constituent parts, size, weight, and manufacturing costs thereof.